This invention relates to semisubmerged high-speed vessels, and more particularly to vessel hull structures and hull equipment designed to make the vessel oscillationless. The vessel is an oscillationless vessel of the type in which a mono-lower hull or twin-lower hulls under water and an upper hull above water are connected by way of struts.
It is a universal requirement of transportation media to carry objects faster, cheaper and in greater quantities. In the marine transportation business, the fulfilment of these requirements has been an ever continuing goal from ancient times. The same goal has been sought also in the shipbuilding industry. In particular, to increase the speeds of vessels is the biggest requirement of naval architectural technology. Recent remarkable progress in aeronautical engineering makes the requirement of vessel speed urgent.
High speeds of a vessel such as 30 Knots to 40 Knots have already been realized by warships. However, it has not yet been achieved by merchant vessels in navigating for a long time across the ocean.
Vessels are subjected to large oscillations due to waves during navigation in oceans. When the oscillation generates an acceleration of more than (1/2)G, the human body cannot endure this motion for a long time, and further, the hull, machinery and equipment are also likely to be damaged.
The duration of high speed navigation of warships is limited. Therefore, the oscillation problem of a warship has been solved by using hull, machinery and equipment which can endure the problem during this limited time and also by training the crews.
For a merchant vessel, however, whose business is to transport, the problem cannot be solved in the same way as that for warships. A vessel which can carry objects for a long time at high speed without oscillation in waves is desired. As a method to control oscillation in the conventional displacement mono-hull vessel, the use of bilge keels or movable foil stabilizers has been tried but sufficient stabilization has not yet been obtained. In particular, it has been impossible to control the pitching oscillation. As long as the vessel has self-stabilizing ability, the vessel is inevitably subjected to large heeling forces and heel recovery forces which oscillate the vessel.
It has been considered to use a submarine as a merchant cargo vessel. A submarine does not oscillate and has a high propulsion efficiency at high speed, but it has a risk of safety in the deep sea water and needs a lot of ballast to sink in water when it carries cargoes lighter than water. Further, the cargo space is limited under water and thus it is extremely not uncommon as a merchant vessel.
As one development of modern shipbuilding technology, hydrofoil vessels have appeared. .Since these vessels have no self-stabilizing ability in a state of cruising, no oscillation takes place when a vessel is subjected to waves, but it cannot be a large vessel because the area of the foil is limited to support the vessel weight. Recent air cushion vehicles called ACV including hover craft and surface effect ships have a high propulsion efficiency such as to achieve a high speed of almost 100 Knots. The ACV, however, has a weak point in maneuverability and thus it is not suitable for navigation in waves as a merchant vessel.
Catamaran type vessels have been considered. Originally, the twin hull vessel was just a combination of two conventional displacement mono-hull type vessels. In order to improve the propulsion efficiency, the vessel movability and carriability of cargo, a vessel called SWATH which means Small Waterplane Area Twin Hulls is becoming popular.
SWATH consists of two lower hulls under water, an upper hull above water and struts connecting these. SWATH navigates in a semisubmerged state and this vessel receives the buoyancy force derived from the displacement of the submerged hulls. Thus the scale up to a large vessel can be easily done and the cargo can be carried on the upper hull without limitation. However, as long as self-stabilizing ability is needed for the SWATH, SWATH cannot avoid oscillation. And also it causes big trouble that SWATH has the submerged hulls in the shallow draft state.
An Extended Performance Hydrofoil vessel called EPH which navigates in a semisubmerged state has also been considered. EPH is equipped with mono buoyancy tank and hydrofoils. EPH has no self-stabilizing ability in a state of cruising, and therefore EPH is an oscillationless vessel. But it causes big trouble that EPH has a submerged hull in the shallow draft state.
The submerged hull generates large wave exciting forces at hull shape changes during navigation in the shallow draft state. The vertical component of the wave exciting force is the wave heaving force. The wave heaving force is a source of oscillation of the vessel. End structures including struts at the fore and aft of the vessel form hull shape changes parts and can be a source of wave heaving force which may cause the oscillation of the vessel particularly in the longitudinal direction. Further a high-power propelling means of the multi-axial type concentrated at the aft part forms a hull shape change and can be a source of a large wave heaving force causing a longitudinal oscillation of the vessel.
The foregoing is the background of the pursuit of the oscillationless ocean going vessel of the type according to this invention.